Mac hardware advice

I need to replace my mid-2011 27" imac due to a failing screen and I've been looking at used late-2015 imacs.

If you have any experience with late 2015 models, can you tell me if there's a substantial difference in the FCPX or Premiere Pro editing experience between the i7 4GHz option and the i5 3.3GHz option?

Let's assume I'm using an external RAID-0 setup via USB 3.0 and have enough RAM and nothing else getting in the way. How important is CPU clock to editing? And I don't really understand the material advantages between the i5 and i7 lines. My current system has an i7 3.4GHz.